Spinel-type lithium manganese composite oxides and lithium cobalt composite oxides are known as positive electrode active materials of lithium ion secondary batteries. Spinel-type lithium manganese composite oxides have a problem that compared to lithium cobalt composite oxides, their capacities are more degraded when repeatedly charged and discharged under a high temperature environment. In order to solve this problem, improvement of the crystal structure of the lithium manganese composite oxides is effective. The crystal structure can be improved by substituting a portion of Mn of the lithium manganese composite oxide with a foreign metal. It is known that Al is suitable as the foreign metal.
On the other hand, spinel-type lithium titanium composite oxides are known as negative electrode active materials of lithium ion secondary batteries. Spinel-type lithium titanium composite oxides are negative electrode active materials having high structure stability and high reliability, but are known to have a problem that they emit gas during operation of the battery.